Hybrid vehicles that comprise a hybrid drive are known from the prior art. In addition to the internal combustion engine they comprise at least one electric machine. In serial hybrid vehicles a generator is driven by the internal combustion engine and the generator supplies electrical energy to the electric motor that drives the wheels. In addition, parallel hybrid vehicles are known, in which the torques of the internal combustion engine and at least one electric machine that can be connected to the internal combustion engine are added. In this case the electric machine can be connected to the belt drive or to the crankshaft of the internal combustion engine. The torques produced by the internal combustion engine and/or the at least one electric machine are transmitted to the driven axle by a downstream transmission.
For example, from DE 102006019679 A1 a drivetrain having an electrically adjustable hybrid transmission and an electro-hydraulic control system, several electric power units and several torque transmission mechanisms is known. In this, the torque transmission mechanisms can be selectively engaged by the electro-hydraulic control system in order to provide four forward gears, a neutral condition, an electric mode of operation with lower and higher speed, an electrically adjustable mode of operation with lower and higher speed, and an uphill operating mode.
From DE 102005057607 B3 a hybrid drive for vehicles is known, containing at least a main motor, in particular an internal combustion engine, a generator, an electric motor and a planetary transmission comprising a sun gear, a ring gear, a planetary gear carrier and planetary gears, which has at least one drive output shaft. In this case it is provided that for a first driving range of the vehicle, to add the torques, the output shafts of the main engine and the electric motor are coupled to the sun gear of the planetary transmission, and for a further driving range one of the two motors can be coupled with positive interlock to the ring gear of the planetary transmission for the mechanical addition of the speeds in accordance with the superposition principle.
In vehicles with an automated transmission, the transmission input must be free from load before a gear can be disengaged; furthermore, the transmission input must be synchronized before a new gear can be engaged.
According to the prior art, in hybrid vehicles with an automated transmission a shift operation with traction force interruption takes place during hybrid operation in that, in a first step, the load is removed at the internal combustion engine and the electric machine, and the internal combustion engine is then decoupled from the drivetrain by disengaging a clutch. When the internal combustion engine has been decoupled the old gear is disengaged, the speed of the electric machine is adjusted to the synchronous speed, the new gear is then engaged and the internal combustion engine is coupled, and finally the load on the internal combustion engine and the electric machine is built up again.
In a patent application by the present applicant with the same timing as the present application, a method is described for carrying out a shift operation with traction force interruption during hybrid operation in a parallel hybrid vehicle comprising an automated transmission, in which the internal combustion engine and the electric machine remain coupled to one another and the load is removed by operating the electric machine before the old gear has been disengaged and before synchronization to the new gear.
In this case it is proposed in particular, in order to remove the load before the old gear has been disengaged, to operate the electric machine in such manner that it compensates the torque of the internal combustion engine while the internal combustion engine is operated at constant torque during the load compensation, and only to act upon the torque of the internal combustion engine if it exceeds a threshold value or if the electric accumulator of the vehicle would become too fully charged by the electric machine due to the load compensation. When the load has been removed the old gear is disengaged and synchronization to the new gear is carried out by adjusting the speed of the electric machine to the synchronous speed of the new gear. The speed adjustment of the electric machine is preferably carried out in a speed regulation mode to which the electric machine is changed, with the torque of the internal combustion engine serving as a pilot torque for the speed regulation of the electric machine.
With the method described, if the electric machine fails or the energy accumulator of the hybrid vehicle is fully charged the situation can arise that in upshifts, in particular traction upshifts, it is no longer possible to remove the load or synchronize the transmission input. As a result the shift operation takes a very long time, and this is unacceptable for reasons of both comfort and driving safety.
Furthermore, delays can also occur during a downshift when the electric machine is not available.